Imidazolium-based poly(ionic liquid)s grafted on the surface of multiwalled carbon nanotubes (MWNTs) were prepared by Diels-Alder “click” reaction with a high grafting density. Poly(styrene-alt-maleic anhydride) (PSM) was functionalized with furfuryl amine and then it was modified with 1-(3-aminopropyl)-3-methylimidazolium bromide to produce poly(ionic liquid)s functionalized with furfuryl groups (PSMF-ILs). PSMF-ILs were directly grafted onto the surface of MWNTs under ultrasonication to form PSMF-IL/MWNT nanocomposites. The material was characterized by FTIR, Raman spectroscopy, XRD, XPS and TEM analyses. The results showed that a very high grafting density was achieved in deep eutectic solvents based on choline chloride:ethylene glycol in a short time.